1. Field of the Invention
The present invention relates to a circular path control apparatus and method for improving accuracy of the circular path of a multi-axis servomechanism for use with NC machine tools, laser processing machines, etc.
2. Description of the Prior Art
With a multi-axis servomechanism for use with NC machine tools, laser processing machines, etc., it is essential to minimize the amount of path error in the path control of a tool in order to ensure an excellent processing accuracy.
In a known type of control apparatus for multi-axis servomechanisms used with numerically controlled machines, the desired tool path control is effected by producing a position command for each shaft as a function of time, detecting the present position of each shaft by a position detector and independently controlling each shaft by a variable-value control employing a feedback control.
However, this type of path control for the multi-axis servomechanism is disadvantageous in that the control is independently effected by providing the desired value as a function of time for each shaft so that in the case of a high-speed feed drive of a circular path, even if the servo characteristics of the driving shafts are the same, their delays in response are not the same due to the variations in rate of change of command value among the shafts and an error is caused between a command circular path and the actual response path, thereby making it impossible to ensure an excellent processing accuracy.
In an attempt to solve these problems, a command generating method for multi-axis servo systems is disclosed in Japanese Patent Laid-Open No. 60-231207. The method disclosed in this publication is designed so that in the case of a multi-axis servomechanism involving two or more axes, a position command and a speed command for the principal shaft is generated as a function of time and a position command and speed command for the auxiliary shaft are generated as functions of the condition of the principal shaft.
However, this command generating method for multi-axis servomechanism is disadvantageous in that the positions and speeds of the auxiliary shaft are stored as function values of the positions of the principal shaft and thus a control apparatus must have a huge memory capacity.